Concomitant with recent developments in electronic techniques, a reduction in size and an increase in capacitance of multilayer ceramic capacitors have increasingly advanced.
This type of multilayer ceramic capacitor is manufactured by the steps of forming a ceramic laminate by alternately laminating internal electrodes and dielectric layers each composed of a dielectric ceramic containing BaTiO3 or the like as a primary component, performing a firing treatment on the ceramic laminate to form a multilayer sintered body, and forming external electrodes on external surfaces of the multilayer sintered body. When the thickness of the dielectric layer is decreased and when the number of the dielectric ceramic layers is increased in this multilayer ceramic capacitor, a reduction in size and the increase in capacity of the ceramic electronic capacitor can be realized.
However, when the thickness of the dielectric layer is decreased, a voltage having a high electric field strength is applied thereto. Hence, a decrease in the relative dielectric constant ∈r and a degradation in temperature properties may occur, and in addition, a dielectric breakdown between internal electrodes may also occur, so that the reliability may be degraded in some cases.
Accordingly, a multilayer ceramic capacitor has been, heretofore, proposed (Patent Document 1) in which, for example, the dielectric layers and internal electrodes are integrally laminated to each other; the dielectric layers are each composed of a sintered body of ceramic grains; the ceramic grains are in the form of a solid solution; the ceramic grains each contain at least one rare earth element selected from Ho, Sc, Y, Gd, Dy, Er, Yb, Tb, Tm and Lu; and the concentration of the rare earth element is designed to increase from the center of each of the ceramic grains toward its grain boundary.
In addition, a multilayer ceramic capacitor has also been disclosed in this Patent Document 1 in which at least one acceptor type element selected from Mn, V, Cr, Co, Fe, Cu, Ni and Mo is contained in the ceramic grain, and the concentration of the acceptor type element is designed to increase from the center of the ceramic grain to its grain boundary.
According to Patent Document 1, the grain diameter can be made smaller since the acceptor type element or the rare earth element is designed to have a concentration gradient increasing from the center of the ceramic grain to its grain boundary. Hence, the reduction resistance and oxidation resistance of the dielectric layer are improved, the electrical resistance of the ceramic grains forming the dielectric layer is increased, and the reliability, more specifically, the reliability obtained when the thickness of the dielectric layer is decreased, can be improved.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2001-230148 (Claims 1 and 4)